1. Field
Example embodiments relate to pastes for photoelectric conversion layers of X-ray detectors, X-ray detectors including photoelectric conversion layers, and methods of manufacturing the same.
2. Description of the Related Art
X-rays, which have a wavelength between visible rays and gamma rays, can penetrate solid objects. The penetration amount of X-rays depends on the density of the inside of the solid objects. Images of the interior of an object are created by measuring the amount of X-rays that penetrate the object.
In one conventional example, photosensitive films are used to record X-ray images. An alternative is known as digital radiography (DR) in which X-ray images are taken by using X-ray detectors.
Conventionally, flat panel systems including semiconductors are used as X-ray detectors. Flat panel systems have a structure based on thin film transistor (TFT) active matrix arrays. Conventional flat panel systems are classified as indirect conversion-type and direct conversion-type systems.
A conventional indirect conversion-type flat panel system utilizes a scintillator and a photodiode composed of amorphous silicon (a-Si), whereas a conventional direct conversion-type flat panel system utilizes a photoconductive material such as amorphous selenium (a-Se).
In a TFT active matrix array, electric charges are generated by X-rays and stored in a capacitor. The electric charges are read as a signal using a multiple-receiving method in which the signal of each column of the array is received by a peripheral circuit unit with rows being switched one by one.
An conventional indirect conversion-type a-Si flat panel system includes an a-Si TFT, a PIN photodiode composed of amorphous silicon, and a scintillator. In this flat panel system, the scintillator absorbs irradiated X-rays, thereby generating visible rays. The photodiode detects and converts the visible rays into an electric signal and stores the electric signal. The stored electric signal is read by operation of the a-Si TFT. However, the a-Si flat panel system requires a relatively complicated manufacturing process. Moreover, reducing the resolution of the a-Si flat panel system to below 100 μm is relatively difficult due to light spreading by the geometric structure of the scintillator.
Recently, research into flat panels using amorphous selenium (a-Se) as a photoconductive material has been conducted with regard to direct conversion-type flat panel systems. However, application of a relatively high voltage (e.g., thousands of volts) is needed to activate the amorphous selenium. Moreover, amorphous selenium requires relatively high energy for forming electron-hole pairs. Also, the atomic weight of amorphous selenium is smaller than that of other semiconductor compounds. Thus, formation of a relatively thick a-Se layer is needed to achieve relatively high luminous efficiency of the flat panel.